Porth yr Ogof is a cave located near the village of Ystradfellte, near the southern boundary of the Brecon Beacons National Park in Wales. It lies on the course of the Afon Mellte, a river whose name translates as ‘lightning’, commonly explained as a reference to the flashy' nature of the river, i.e. rising and falling rapidly in response to rainfall. In 1998 the cave's passageways had been measured as over in length. Among the cave's fifteen entrances is the largest cave entrance in Wales and one of the largest in the UK standing at nearly wide and high. The cave was used as a show cave many years ago, but it does not have the attractions of more decorated caves such as Dan yr Ogof, and so todaythe cave is more often used to introduce people to the enjoyment of the exploration of caves.
Inside the cave
Entry to Porth yr Ogof is most often made through the wide Main Entrance, either using a dry ledge on the left or by wading through the knee-deep river to the centre and right. The second most used cave entrance is called the Workman's or Tradesman's Entrances. A passage in the left of this entrance which leads to a mud cavern. Cavers are presented various challenges inside, including the Wormhole, the Letterbox and the Creek, home to 'Death Ledge' which is further inside the cave. There are also two features named the Washing Machine – both feature large expanses of water. Porth yr Ogof is now uncommercialised, and is used as a learning resource for caving. Along with the other attractions in the cave, two short potholes are easily accessible by amateur potholers. The cave is generally wet, however; White Horse Pool, named so because of the shape of the calcite deposit on the back wall, is several metres in depth despite the shallowness of the edges, and there are many sumps, the majority of which exist in the portions of the cave north of the Tradesman's Entrance.
Deaths
There have been eleven deaths at Porth yr Ogof since 1957, and all but one have lost their lives in the cold, fast-flowing and deep Resurgence Pool at the far end of the cave where the Afon Mellte resurges.
'Porth yr Ogof' is Welsh, and is best translated as 'gateway to the cave'.. The cave lies in the valley of the Afon Mellte and is located in a comparatively narrow band of Carboniferous Limestone. Except after periods of heavy rain, the river bed is largely dry downstream of Ystradfellte, the river only rising to the surface again just before the cave. The cave has been known to humans for many centuries, as it is not easily overlooked once one is in the valley, but because of the passageway's susceptibility to severe flooding there has been no evidence found of any prehistorichuman habitation. The cave and its many visible fossils were mentioned in the writings of Edward Lhuyd, and in the 19th century it was mentioned again by the first pioneers of caving.
